The present disclosure relates flow of a process fluid in an industrial process. More specifically, the present disclosure relates to cooling in a manifold for a process variable transmitter.
In oil refineries the use of orifice plates, averaging pitot tubes, or the like to measure flow is a common practice. Some process fluid being measured may be at temperatures of approximately 700° F. and often solidifies below approximately 200° F. Process variable transmitters that measure and communicate flow rates and other variables have electronics that typically cannot operate at temperatures above about 200° F. Because of this, direct mounting or close coupling of a process variable transmitter to a process flow pipe cannot be accomplished due to overheating of the transmitter electronics caused by the high temperature of the process fluid. To alleviate the overheating of transmitter electronics, process variable transmitters are often located some distance away from process fluid piping.
To separate transmitter electronics from the process piping, small bore impulse piping may be used Impulse piping often requires junctions and joins, and can be difficult to maintain without leak points in the impulse piping connections. Further, as the amount of process fluid in a small bore pipe is small, process fluid temperatures can drop rapidly in impulse piping. When a process fluid in a pipe, especially in a small bore pipe, is at a higher temperature than the air surrounding it, heat passes through the wall of the pipe from the process fluid to the surrounding air. This heat loss will cause the temperature of the process fluid to fall.
Certain process fluids will solidify if the temperature drops below a specific threshold. For example, at a temperature of about 200° F., heavy crude typically solidifies. Other process fluids may solidify at different temperatures. This is a problem when measuring pressure and the process fluid solidifies in the measurement impulse line.
To reduce the chances of solidification of process fluid in impulse piping, which can create a blockage, low pressure steam (on the order of 30 pounds per square inch) is used for steam tracing in some environments. Steam is typically available as a utility in the area of process flow measurement. Steam trace pipes are small bore pipes that are run next to or in close proximity to impulse piping, and contain pressurized steam at a certain temperature, often about 212-230° F., that assists in maintenance of the temperature of process fluid in the impulse pipes high enough to prevent their solidification.
Precipitate accumulation is another common cause of blockage in impulse piping. Solids in a flow stream will have a tendency to accumulate at the lowest point in an impulse tube arrangement. Impulse tubing is often plumbed around and over obstacles, such as by using elbows and traps, resulting in many areas where solids can collect.
Further, process leaks in impulse tubing may result in erroneous readings at a process variable transmitter, such as erroneous differential pressure readings, and can have a significant effect on flow measurement accuracy. The potential for a leak in a differential pressure flow measurement system is directly proportional to the number of connections in the system.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.